YARN-781. Exposing LOGDIR in all containers' environment which should be used by containers for logging purposes. Contributed by Jian He.
svn merge --ignore-ancestry -c 1493428 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1493429 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-2' into branch-2-gd
Merge remote branch 'origin/branch-2-gd' into fb-HADOOP-7435-branch-2-gd